Originally the system has one local disk /dev/sda, then connected with a new external storage (a storage array or a fiber-channel or a SAS disk). After the system was booted up, the internal disk on the server were changed to /dev/sdb while the external disks on the fiber storage were now /dev/sda.
Red Hat Enterprise Linux All Verisons
The reason is kernel load different drivers in different order, the first loaded get the name /dev/sda.
If the two ...